In recent years, recycling of waste refuse has advanced rapidly. In this connection, plastics consumed as raw material for plastic products are thought to be mostly vinyl chloride type resin (hereinafter referred to as PVC), polyethylene type resin (hereinafter referred to as PE), and polypropylene type resin (hereinafter referred to as PP) and polystyrene type resin (hereinafter referred to as PS) and it is thought that waste plastics that are collected are mostly the aforesaid resins. And when these resins are to be recycled, it is necessary to sort the resins according to kind.
A method for sorting a mixture of chips of said kinds of plastics will now be described with reference to FIG. 14.
That is, there is a technique in which first, crushed chips 1 of a plurality of kinds of plastics are charged in a frictional charging device 2. Thereafter, the charged plastic chips 1 are fed from the frictional charging device 2 to an electrostatic separator 3 used for sorting, where particular plastic chips 1 are separated.
Said frictional charging device 2 is in the form of a cylindrical vessel 5 having a loading port 6 formed at one end thereof and a delivery port 7 at the other end. Rotatable stirring vanes (not shown) are installed in said cylindrical vessel 5, and a loading hopper 8 is installed at said loading port 6.
Further, said electrostatic separator 3 comprises a metal drum electrode 10 rotatable around a horizontal axis in a predetermined direction, and an arcuate opposed electrode plate 11 extending in the direction of rotation of the metal drum electrode 10 and disposed obliquely above and opposed to the latter. The opposed electrode plate 11 has a negative output of a high voltage source 12 connected thereto, while a positive output of the high voltage source 12 is grounded. As a result of this connection, a rotary grounded electrode is formed on the metal drum electrode 10 and a sorting electrostatic field is formed between the metal drum electrode 10 and the opposed electrode plate 11.
Disposed below the metal drum electrode 10 are first and second upwardly opened separation vessels 13 and 14 arranged in the order mentioned as seen from upstream of the direction of rotation. Further, disposed on the outer periphery of the metal drum electrode 10 is a brush 15 for scraping off plastic chips 1 sticking to the peripheral surface of the metal drum electrode 10.
The function of the above arrangement will now be described.
The chips 1 of a plurality of kinds of plastics are loaded through the loading hopper 8 into the cylindrical vessel 5, where the chips 1 of said kinds of plastics are stirred to be rubbed against each other by the stirring vanes rotating therein, whereby they are frictionally charged. The plastic chips 1 thus charged are delivered from the delivery port 7 and fall onto the metal drum electrode 10. And the positively charged plastic chips 1 are repelled by the metal drum electrode 10 and drawn toward the opposed electrode plate 11 and fall into the first separation vessel 13. Further, the negatively charged plastic chips 1 are drawn toward the surface of the metal drum electrode 10 and either fall into the second separation vessel 14 with the rotation of the metal drum electrode 10 or are scraped off the surface of the metal drum electrode 10 by the brush 15 and thereby separated and fall into the second separation vessel 14.
In the aforesaid sorting of plastic chips 1, the following has been proposed in order to sort out particular plastic chips 1 with higher accuracy and recover them.
That is, in order that chips 1 of a particular kind of plastic to be sorted out and plastic chips 1 having a reverse polarity to that of said chips 1 of said particular kind of plastic, in the electrification rank for said kinds of plastics forming the chips 1, may be equal in proportion to each other, particles of either of said plastics should be put as a friction assisting material in the stirring vessel 5.
For example, if said kinds of plastics forming the chips 1 are PVC, PE, PP, PS, these plastics may be arranged in order of electrification rank as PS.fwdarw.PE.fwdarw.PP.fwdarw.PVC. Here, PS is on the positive side of the electrification rank and PVC is on the negative side of the rank. This shows that PS and PE, when electrified, have a greater amount of positive charge and that PP and PVC, when electrified, have a greater amount of negative charge. Therefore, in the case where, e.g., PVC is to be sorted out, if the amount of PVC is smaller than the total amount of PS and PE, particles of PVC are put as a friction assisting material in the cylindrical vessel 5 such that the amount of PVC is equal to the total amount of PS and PE that are on the positive side of the electrification rank and have a polarity reverse to that of PVC. Further, on the contrary, if the amount of PVC is larger than the total amount of PS and PE, particles of PS and PE that are on the positive side of the electrification rank and have a polarity reverse to that of PVC, are put as a friction assisting material in the cylindrical vessel 5. Thereby, PVC is sufficiently electrified in a short time to negative polarity, so that PVC can be sorted out with high accuracy in the electrostatic separator 3.
However, as described above, in the case where the friction assisting material has been put in the cylindrical vessel 5, the friction assisting material is also delivered through the delivery port 7 of the cylindrical vessel 5 together with the plastic chips 1, so that there is a problem that a special device is required to recover the delivered friction assisting material and put it back again into the cylindrical vessel 5.
As a means for solving the above problem, the following arrangement may be contemplated. That is, a friction assisting material 18 of larger particle size than that of plastic chips 1 is used and a net member 16 of orthogonal cross pattern is fixedly attached to the delivery portion 7 of the cylindrical vessel 5. As shown in FIGS. 15 and 16, the meshes 17 of this net member 16 are larger than the plastic chips 1 and smaller than the friction assisting material 18. The friction assisting material 18 is thus confined in the cylindrical vessel 5, whereby the friction assisting material 18 can be repetitively used.
In the conventional arrangement described above, however, as shown in FIG. 15, even if the meshes 17 of the net member 16 are made larger than the plastic chips 1, there occurs a problem that such plastic chips 1 are caught by the intersections between the mutually orthogonal wires 16a and 16b of the net member 16 and gradually clog the meshes 17 of the net member 16 until troubles occur in delivering the charged plastic chips 1 from the delivery port 7.
Further, as shown in FIG. 16, when plastic chips 1 are about to pass through the meshes 17 of the net member 16 for delivery from the delivery port 7, particles of the friction assisting material 18 traveling to a point just short of the net member 16 together with plastic chips 1 block up the meshes 17 of the net member 16, presenting a problem that delivery of plastic chips 1 becomes stagnant.
Accordingly, an object of the present invention is provide a frictional charging device wherein a friction assisting material is repetitively used, whereby particular plastic chips are fully charged in a short time and the charged plastic chips can be delivered without any trouble.